VECURONIUM NEUROMUSCULAR BLOCKADE REFLECTS LIVER-FUNCTION DURING HEPATIC AUTOTRANSPLANTATION IN PIGS

Background: Rapid assessment of hepatic function early after reperfusi on of the liver graft is of great importance,because it may allow for prompt detection of incipient hepatic graft failure. The current study was undertaken to determine whether the continuous recording of neuro muscular transmission could be used as an on-line assessment of hepati c function during liver transplantation when a muscle relaxant with hi gh hepatic uptake is used. Methods: We quantified and compared the eff ect of liver exclusion and graft reperfusion on the level of vecuroniu m-induced neuromuscular blockade in nine pigs studied twice within 3 d ays. During the Ist day (control session), an intravenous infusion of vecuronium was administered to maintain a constant 90-95% twitch depre ssion during 180 min. The twitch response was then allowed to recover spontaneously to 75% of its prerelaxant value. Neuromuscular transmiss ion was continuously measured on the right anterior leg using an accel eration transducer. During the same time period, the metabolic rate of C-14-labeled aminopyrine (a well-established quantitative test of the liver microsomal function) was determined by measuring the excretion of (CO2)-C-14 in expired air after administration of an intravenous bo lus of C-14-labeled aminopyrine. Two days later, the pigs underwent a hepatic autotransplantation, during which vecuronium was administered to maintain a constant 90-95% twitch depression. After reperfusion of the liver graft, the vecuronium infusion rate was maintained at its an hepatic level, and the recovery index of the neuromuscular blockade (t he time from 25% to 75% recovery of twitch height) was calculated. The aminopyrine breath test was performed during the last 30 min of the a nhepatic phase, and during 3 h after reperfusion of the liver graft. R esults: During control studies, the mean infusion rate of vecuronium w as 1.30 +/- 0.33 mg.kg(-1).h(-1) and the recovery index was 3.4 +/- 0. 5 min. During liver dissection, the infusion rate of vecuronium was si milar to the control value (1.18 +/- 0.16 mg.kg(-1).h(-1)), then consi derably decreased to 0.05 +/- 0.03 mg.kg(-1).h(-1) during the anhepati c phase. After reperfusion of the liver graft, the recovery index was markedly prolonged to 35.5 +/- 15.8 min, indicating a prolongation of the recovery of neuromuscular blockade by a factor of 10.4. Excretion of (CO2)-C-14 was equal to zero during the anhepatic phase and then in creased to 0.19 +/- 0.11% during the Ist h after reperfusion of the li ver graft, an excretion rate corresponding to 11.2% of control conditi ons. The relationship between individual changes in the recovery index of the neuromuscular blockade and (CO2)-C-14 excretion in expired air after reperfusion of the liver graft showed a strong significant corr elation (r(2) = 0.71). Conclusions: These results indicate that, compa red with the control studies, there is a similar decrease in the recov ery rate of vecuronium-induced neuromuscular blockade and in the metab olic rate of C-14-labeled aminopyrine during the progressive recovery of hepatic function immediately after unclamping of the liver vessels. Metabolism of C-14-labeled aminopyrine increased progressively during the reperfusion phase. Therefore, recording of neuromuscular transmis sion during liver transplantation could serve as a continuous and easy to perform assessment of liver graft function provided that a muscle relaxant with a high hepatic uptake is used for neuromuscular blockade .